1. Field of the Invention
This invention relates to ultrasonic transducers for performing inspections of the interior of metals, and more particularly to an ultrasonic transducer applicable to accurately inspect the interior of metal objects such as steel pipe having complex irregular surface areas.
2. Description of the Prior Art
A preliminary patentability and novelty search conducted in connection with the invention forming the subject matter herein revealed the existence of the following United States patents:
______________________________________ 4,541,064 4,663,727 4,691,572 4,700,572 4,872,130 4,995,320 5,043,663 ______________________________________
The patents listed above are representative of the abundance of prior art patents that relate to the general subject of non-destructive testing or inspection of hollow cylindrical steel members, such as lengths of steel pipe used for containment of hot water and steam in atomic energy electric generating plants, boilers of the type used for generating steam for use in steam turbines for generating electricity, and steel tubing for well drilling, pumping and well casing, particularly in the oil and gas industry. Some of the physical characteristics tested for include wall thickness, there being very close tolerances regarding adherence to internal and external diameters, voids within the interior of the metal wall, cracks of various kinds, including circumferential, angular and longitudinal cracks that are difficult or impossible to detect by a mere visual inspection of the exterior or interior surface of the tubing or pipe. The reason it is important to detect and eliminate or repair tubing or pipe lengths having such defects stems from the fact that inclusion of a defective length of tubing or pipe in an installation may result in a rupture of the tubing or pipe, possibly resulting in catastrophic property damage, and perhaps even the loss of life among personnel working in the vicinity of the rupture.
As will be seen from the teachings of the patents listed above, such testing and inspection is frequently accomplished through application of ultrasonic technology. The broad concept of the utilization of ultrasonic wave energy for the detection of flaws within the interior of a body is of course an old concept in the prior art. The concept has been used to test lengths of rails to determine the existence of flaws to thus increase the reliability of railroad tracks. In more recent times, the concept has been combined with computer technology to provide visual and printed displays of the location and extent of "flaws" in such diverse objects as steel tubing, conduit, pipe lengths, and even the human body, where abnormalities within the body may be discovered without invasive surgical procedures.
In the area of testing and inspection of elongated lengths of steel tubing or pipes for flaws, such inspection may occur following manufacture and before installation, or it may occur after installation and use for a finite time followed by removal for the express purpose of inspection for damage that might having ocurred during installation or use, and prior to reinstallation. Thus, referring to U.S. Pat. No. 4,541,064, there is taught a method and apparatus for ultrasonic testing of tubular goods to discover the presence of defects, to determine the orientation of the defect, i.e., circumferential, angular or longitudinal, to determine its extent, and to display the defect through use of computer technology. The process proceeds without the need to rotate either the inspection head or the tubular goods being inspected. Instead, the inspecting head includes a full coverage transducer collar having arrays of ultrasonic transducers positioned to test for longitudinal, transverse and wall thickness defects, the transducers being operatively connected to a computer system programmed to display and or record the location, type and extent of the flaws as the transducer collar and test piece move relative to one another.
U.S. Pat. No. 4,663,727 in like manner teaches the use of an ultrasonic inspection apparatus for inspecting the condition of steam generating tubes from the interior of the tubes following insertion of and bonding of a repair sleeve within the tube. Inspection is for the purpose of discovering voids in the bonding, and is accomplished by a probe equipped with ultrasonic transducers, the probe being advanced internally longitudinally along the tube being inspected in increments of 0.032 of an inch and rotated at each plane to perform a circumferential scan of the tube to detect flaws in the bonding. The signals generated by the ultrasonic transducers are received, digitized and processed, with the aid of a programmed digital computer, to graphically display the existence and location of voids.
In U.S. Pat. No. 4,691,572, it is stated that in conventional ultrasonic transducer inspection of metallic objects, there is a requirement for the interposition of an acoustic coupling medium, usually liquid, between the transducer and the wall under inspection. This patent teaches an apparatus for the inspection of pipelines or tubing from the interior thereof, that utilizes "contactless" electromagnetic transducers that eliminate the need for a coupling medium between the transducer and the interior surface of the wall being inspected, while having the capability of generating ultrasonic waves within the material under inspection, for the detection of flaws therein.
U.S. Pat. No. 4,700,572 teaches a method and apparatus for automatic and continuous ultrasonic inspection of elongated steel pipes that are fed successively to the inspection station. The ends of each of the lengths of pipe are detected, the location of flaws in relation to the ends of the pipe are detected, and marking means are applied to the pipe to mark the location of each of the flaws.
U.S. Pat. No. 4,872,130 teaches the utilization of ultrasonic wheel probes comprising rotatably mounted transducer block and yoke assemblies to facilitate rapid adjustment of the helical scan angle of the assembly for use with different sized pipe, inspection of which proceeds through rotation of the pipe in relation to the transducer arrays, which move helically along the pipe from one end to the other. The system is coupled to a pair of computers, one being dedicated to user input/output, while the second computer controls real-time processing of ultrasonic data received from the transducers. The system has the capability of indicating pipe status through use of automatic color-coding, graphic presentation on a computer monitor or through printing of the results of the inspection.
U.S. Pat. No. 4,995,320 is directed to a carriage structure for providing mobility along the length of a steel pipe of the equipment or instruments utilized to effect inspection of the pipe for flaws. One of the advantages claimed for the carriage structure is that it does not surround the pipe but rather moves along the pipe on magnetized wheels that retain the carriage on the pipe, and a drive system that drives the carriage along the pipe longitudinally and which can be controlled to cause the carriage to move circumferentially about the outer surface of the pipe. Flaw detection sensors are stated as being capable of support on the carriage, with appropriate transmission of the signals from such flaw detector sensors to a signal converter and a data processing device, where the data regarding the flaws are processed, and presumably displayed and/or printed.
U.S. Pat. No. 5,043,663 is directed to a method and apparatus for detecting and displaying or printing the existence, location, and extent of all defects in a tubular member. A rotatable head supporting a multiplicity of transducers is caused to move along the length of the tubular member. Signals from the transducers are processed, preferably by a computer system, and indicate the presence of flaws and their physical characteristics. Longitudinal and circumferential position detectors cooperate with the transducers and the computer processing equipment to indicate the location and configuration of the defects in the tubular member.
It is significant to note that in all of the prior art patents listed above, and in known conventional inspection procedures, testing or inspection proceeds along surfaces that are smooth, i.e., surfaces that do not contain abrupt changes in direction or other surface irregularities. There is good reason for this phenomenon. The reason is that ultrasonic inspection of materials utilizing ultrasonic transducers that are in physical contact with the material under test, with or without a couplant, is carried out using transducers that generate a beam which is related to the surface of the material under test by a fixed angle. If the angle of the surface impinged by the beam changes abruptly, but the transducer generated beam angle does not change to compensate for the change in surface angle, the angle of the beam transmitted through the member under test and reflected back from a flaw or the opposite surface is also changed, resulting in portions of the material from which the member is fabricated to remain unexamined or not inspected, or inspected in an inferior manner, thus reducing the level of reliability of the test.
Accordingly, one of the important objects of the present invention is the provision of a method and apparatus for the accurate and reliable ultrasonic inspection of materials having irregular surfaces.
It is surprising that we have not discovered in the prior art any teaching of an ultrasonic transducer inspection system or apparatus in which the transducer ultrasonic beam direction of transmission is automatically altered when the surface angle of the member under test changes, to thus maintain constant the angle at which the ultrasonic beam penetrates the member under test and is reflected back from a flaw or the opposite surface. Accordingly, it is an important object of this invention to provide an ultrasonic transducer assembly possessing this capability.
Still another object of the invention is the provision of a variable angle ultrasonic transducer assembly which achieves angle variation in a simplified and novel configuration, utilizing the properties of a liquid ultrasonic couplant to provide a usable "footprint".
A still further object of the invention is the provision of a contact type ultrasonic transducer assembly which, when used in conjunction with an appropriate computer-driven scanning system, is capable of generating ultrasonic beams in the material under test at angles which are continuously variable during the course of the examination to compensate for irregularities in the surface of the material, thereby maintaining the beam angle transmitted through the material and reflected back at a constant angle, thus precluding failure to scan sections of the material.
Heretofore it has not been possible to adequately inspect tubular materials having irregular concentricity or variable wall thickness, such as tubular members having pipe weld overlays or pipe fittings such as reducers, couplings or valves and forgings. Accordingly, it is yet another object of the invention to provide an ultrasonic transducer assembly capable of generating a continually variable beam angle to accommodate irregularities of the type noted in the surface configuration of the member under test.
A still further object of the invention is the provision of an ultrasonic transducer operatively mounted for automatic computer-controlled rotational repositioning of the transducer to accommodate surface irregularities in the material being tested.
The invention possesses other objects and features of advantage, some of which, with the foregoing, will be apparent from the following description and the drawings. It is to be understood however that the invention is not limited to the embodiment illustrated and described since it may be embodied in various forms within the scope of the appended claims.